“Her campaign’s approach was to turn out the base as much as possible, and they spent a lot of time trying to churn people out and not so much time on persuasion,” Allen, head of content at the political news website SideWire, told host Bill Tucker on Tuesday’s “America Talks Live.”

“As part of that, she moved to the left . . . [and] there were a lot of people in the Democratic Party that weren’t pleased with her. By moving to the left, she placated some of them but obviously not all of them.

“Not enough Democrats showed up for her in the right places to win the election. . . . Sources in the book talk about her inability to go out, and unwillingness to go out and try to persuade people.”

Allen, whose book is co-written by The Hill’s Amie Parnes and published by Crown, said successful candidates must be able to bridge the divides within their party.

“The left, the center, the right, within their own party, and then attract some other people, so she wasn’t able to do that,” he told Tucker.

“Mostly there was an inability to turn out the hard left that was angry at her . . . and I think she wasn’t able to bring in a lot of those white working-class Democrats who she didn’t really have a message for.”

And why was not she able to convey that message, something her husband, two-term president Bill Clinton was an expert at?

“That’s one of the great inexplicable questions in this campaign,” Allen said. “I mean it was evident to her campaign team that she was having trouble. . . . Our sources told us about a couple situations where she seemed to lose her temper.

“There’s one good story in the book about after her losing the Michigan primary, she kind of turned on one of her top aides. He was criticizing her debate performance, her debate prep performance.

“She was doing her preparatory work on the debate, and he would cut her off and say, that’s not very good, and finally she got tired of it and said, ‘why don’t you try it,’ and she turned around and made him play her, and she kept cutting him off, and telling him he wasn’t doing a very good job.”

Allen added: “The infighting is definitely there, the way that she dealt with her staff, she and her husband reamed them out for not being able to figure out how to get past the email issue . . . and start talking about her economic message . . .

“Clearly what she needed to do was apologize and start that contrition thing with the American public. She just wouldn’t do it.”

Allen said when election results showed she would lose to Republican presidential nominee Donald Trump, her aides tried to convince her to give an impassioned concession speech in which she would promote Democratic values.

He said they wanted her to stand up “for people that she thought would be treated poorly under a Trump administration.”